bcl-2核酶(Ribozyme)促进紫杉醇诱导的细胞凋亡

用核酶技术阻断或降低抗凋亡蛋白 Bcl- 2的表达以促进化疗药物紫杉醇诱导的食管癌细胞凋亡 ,探索克服耐药、提高紫杉醇疗效的新途径 .将特异性切割 Bcl- 2 m RNA的核酶克隆至含MTII启动子并可为 Zn SO4 诱导表达的真核表达载体中 ,通过脂质体转入食管癌鳞状上皮细胞系Eca 1 0 9中 ,经 G41 8筛选得到稳定抗性细胞株 X1 0 9R,挑取单细胞株扩大培养 ,1 40μmol/L Zn SO4诱导 3d,用 Northern- blot、免疫荧光、流式细胞仪鉴定核酶及 Bcl- 2蛋白表达情况 ,用 TUNEL标记及流式细胞术检测凋亡细胞的比例 .bcl- 2核酶在不同单细胞株中有不同程度的表达 ,其中一株X1 0 9R1 4表达最高 .测定其中 Bcl- 2蛋白含量 ,发现 Bcl- 2蛋白表达大为降低 .加入紫杉醇后 ,TUNEL标记及凋亡峰测定结果都表明同一条件下凋亡率升高 .结果提示 ,转入特异性切割 bcl- 2m RNA的核酶可有效地阻断 Bcl- 2蛋白合成 .Bcl- 2蛋白表达降低可明显促进紫杉醇诱导的细胞凋亡 .说明 Bcl- 2蛋白在细胞产生耐药过程中起着重要作用     

层粘连蛋白对晚G1期人胃癌BGC-823细胞生长的促进作用

为研究层粘连蛋白（laminin,LN）促进肿瘤细胞生长作用,采用脉冲标记计数有丝分裂百分率(percentage labeling mitosis,PLM)法测得体外培养人胃癌 (BGC 823) 细胞周期时间为41 h,其中G1期时间为24.5 h. 分裂细胞脱离法获取分裂期细胞,继续培养23 h,在细胞运行进入G1晚期时,将其置于LN 0、0.11、0.55、1.10 μmol/L基质上孵育4 h; 细胞荧光光度计检测晚G1期细胞内Ca2+浓度、钙调蛋白、DNA含量. 结果显示,LN与其膜上受体结合后引起细胞内Ca2+浓度、钙调蛋白、DNA含量增加,尤以在0.55 μmol/L LN作用显著（P<0. 001）.蛋白质免疫印迹分析证明,cPKC α呈现表达,提示 LN与其受体结合可增强其细胞cPKC-α的活性;分析G1期细胞周期蛋白E(cyclinE)、细胞周期蛋白依赖性激酶CDK2表达水平,呈现逐渐增强的趋势; LN可诱导c-Myc蛋白呈现高表达,提示 LN与其受体结合增强与细胞增殖密切相关的基因表达;在LN作用前后的BGC 823细胞均未检测到Bax蛋白表达.结果提示,在人胃癌 (BGC 823)细胞G1/S期交界处,层粘连蛋白与其膜上受体结合引起细胞内Ca2+浓度升高,诱导钙调蛋白的释放,其含量增加,增强蛋白激酶C的活化,导致细胞内DNA含量增加、G1/S期细胞周期蛋白与CDK表达增强、诱导原癌基因c-Myc呈持续表达状态,而凋亡基因Bax不表达.     

RASSF1A对食管癌细胞增殖影响的研究

目的:观察外源性RASSF1A基因对食管癌细胞的增殖作用并探讨机制.方法:将包含RASSF1A基因的质粒转染食管癌细胞EC9706,建立稳定转染细胞克隆,Western blot检测RASSF1A基因表达,通过细胞生长曲线检测细胞生长活性和增殖能力、流式细胞仪检测对细胞周期的影响、裸鼠移植瘤实验检测转染细胞的体内成瘤特性.结果:稳定表达RASSF1A基因的EC9706细胞中RASSF1A蛋白表达增加;细胞生长速度明显减慢;细胞周期中G1/G0期比例明显增加,S期比例减少;EC9706细胞的裸鼠致瘤能力被抑制.结论:RASSF1A基因能显著抑制食管癌细胞在体内外的生长,其机制可能与该基因诱导凋亡、抑制增殖作用有关.     

半边旗二萜类成分PAG通过ROS诱导肝癌细胞凋亡的作用研究

探讨半边旗二萜类成分Pteisolic acid G(PAG)对人肝癌细胞HepG2增殖和凋亡的影响及作用机制。用不同浓度的PAG处理HepG2细胞后,采用MTT法检测细胞存活率;采用PI单染法检测细胞周期分布;采用Annexin V-FITC/PI双染法检测细胞凋亡率;采用RT-PCR和Western Blotting检测细胞内mRNA和蛋白表达情况;采用DCFH-DA法检测细胞内ROS水平,采用ROS抑制剂乙酰半胱氨酸(NAC)评价PAG细胞增殖抑制作用对ROS的依赖性。结果表明,在24 h、48 h和72 h时,PAG可剂量依赖性地抑制HepG2细胞的增殖(p0.05),IC_(50)分别为64.8μmol/L,38.5μmol/L和24.8μmol/L;用药24 h时PAG可剂量依赖性地使HepG2细胞阻滞在G_2/M期,同时增加HepG2细胞凋亡率(p0.05);PAG可剂量依赖性地降低HepG2细胞内Bcl-2 mRNA和caspase 3、PARP、Bcl-2蛋白的表达(p0.05),增加Bax mRNA和actived-caspase 3、cleaved-PARP、Bax蛋白的表达(p0.05)。当使用1 mmol/L的ROS抑制剂NAC预处理HepG2细胞时,PAG对HepG2细胞增殖抑制作用被显著阻断。上述结果表明,半边旗二萜类成分PAG可提高Bax/Bcl-2的基因和蛋白表达比值,从而诱导肝癌细胞HepG2凋亡,该作用可能是通过升高细胞内ROS水平来实现的。     

白藜芦醇对人子宫内膜癌细胞系AN3CA 增殖和凋亡效应 及其机制探讨

目的:探讨白藜芦醇(resveratrol,Res)对人子宫内膜癌细胞AN3CA的增殖抑制和凋亡诱导效应及可能存在的机制。方法:应用噻唑蓝(MTT)法检测Res对AN3CA的增殖影响;流式细胞术检测Res对细胞周期分布和凋亡影响;荧光实时定量PCR检测Res对细胞Bcl-2、Bax和MMP-9mRNA表达水平的影响;Western Blot方法检测Res对PCNA、Bcl-2、Bax及ERK1/2、p-ERK1/2蛋白表达水平的影响。结果:Res对子宫内膜癌细胞AN3CA具有显著的生长抑制作用(P<0.01),呈时间-剂量依赖性;不同浓度Res处理细胞G0/G1期比例显著增加伴随S期细胞数的减少;细胞凋亡率明显增高,200μmol/l Res处理48h凋亡率可达30.96%±2.041%(P<0.01)。与对照组相比,Res能抑制PCNA的蛋白表达量,增加Bax和降低Bcl-2转录和蛋白水平的表达量。Res在短时间内(0.5-1h)激活ERK1/2的磷酸化表达但随着作用时间延长(4-48h)其表现为抑制效应。结论:Res具有抑制AN3CA细胞增殖,诱导细胞G0/G1期阻滞和凋亡的效应。Res诱导凋亡可能是通过上调Bax,下调Bcl-2发挥作用,其抗癌作用机制可能与ERK1/2通路失调相关。     

丙戊酸钠抑制A549细胞生长

目的研究丙戊酸钠对肺癌A549细胞增殖和细胞周期的影响。方法MTT检测生长抑制,流式细胞仪检测细胞周期和凋亡,Western blot检测p21WAF1/CIP1蛋白表达。结果丙戊酸钠以剂量依赖性方式抑制A549细胞生长;丙戊酸钠上调G0/G1期比例,下调S期和G2/M期,不影响细胞凋亡;丙戊酸钠上调p21WAF1/CIP1蛋白表达。结论丙戊酸钠上调p21WAF1/CIP1表达,使细胞阻滞于G0/G1期,抑制A549细胞生长。     

柯里拉京对人肺癌细胞A549的抑制作用及其机制研究

该研究旨在探讨柯里拉京对人肺癌A549细胞凋亡的影响及其潜在作用机制。采用CCK-8细胞活性检测试剂盒检测柯里拉京对A549细胞活性的影响;通过流式细胞术检测细胞凋亡;JC-1线粒体膜电位检测试剂盒检测线粒体膜电位;免疫印迹法检测凋亡相关蛋白(bax、bcl-2、cleaved-caspase-3、cleaved-PARP)的表达量;通过DCFH-DA探针标记检测细胞内ROS水平。研究结果显示,柯里拉京处理能够剂量依赖性地抑制A549细胞的活性,并通过上调bax的表达、下调bcl-2的表达,破坏线粒体膜电位,促进有活性的cleaved-caspase-3以及cleaved-PARP的形成,诱导A549细胞凋亡。活性氧清除剂NAC能够明显逆转柯里拉京诱导的细胞凋亡。因此,柯里拉京可能通过调节胞内ROS水平诱导人肺癌细胞A549发生凋亡。     

F1-V重组亚单位疫苗对鼠疫耶尔森氏菌141强毒株皮下攻毒保护性的研究

在此实验中, 设计了一种包含2种成分的重组融合蛋白作为疫苗成分来防护鼠疫耶尔森氏菌(Yersinia)可能产生的生物威胁. 重组F1-V蛋白与铝佐剂结合, 分别以10, 20, 50 mg剂量免疫BALB/C小鼠, 周期为2个月. 检测小鼠血清抗体水平和T辅助细胞的亚型. 免疫后小鼠以25~600 LD₅₀剂量的鼠疫耶尔森氏菌141强毒株进行皮下攻毒实验. 结果证明, F1-V重组蛋白在 小鼠体内诱导产生足够保护的免疫应答. 血清IgG水平是产生最终保护力的一个重要因素. 20 μg的免疫剂量可以诱导血清抗体效价高达51200, 使小鼠对400 LD50的鼠疫耶尔森氏菌产生100%的保护. F1-V重组蛋白引发的抗体亚型主要为IgG1类, 说明抗体反应趋向Th2型反应. 流式细胞分析表明, 铝佐剂主要帮助F1-V重组融合蛋白诱导强烈的体液免疫而不是CTL细胞免疫应答.表明F1-V重组亚单位疫苗株有希望成为一种新型的鼠疫疫苗候选株.     

FAS/ActD通过线粒体途径引起细胞阻滞诱导人宫颈癌HeLa细胞凋亡

为了探讨FAS抗体与放线菌素D(actinomycin D,ActD)联合作用诱导人宫颈癌HeLa细胞凋亡的分子机制,通过MTT法检测细胞活力,利用流式细胞仪检测细胞凋亡和细胞周期,从而研究FAS/ActD抑制细胞增殖的作用. 结果表明,FAS/ActD能明显降低HeLa细胞的活力,并且通过G1/G0期阻滞和S期阻滞诱导HeLa细胞凋亡. 此外,Western印迹分析进一步显示,FAS/ActD还能引起Bcl-2蛋白表达降低, Bax蛋白表达增加,Bid蛋白发生断裂激活,导致细胞质中Cyto-c释放的增加,并激活在细胞凋亡的执行过程中起着关键作用的caspase 9和caspase 3. 以上结果提示,FAS抗体与ActD的联合作用可能经线粒体途径引起细胞周期阻滞,从而诱导HeLa细胞凋亡. 该研究为宫颈癌的免疫治疗提供了新的思路.     

人重组Fas配体体外诱导细胞周期特异性凋亡模型的建立及其意义

以Molt-4、Jurkat细胞株和外周血淋巴细胞(peripheralbloodlymphocyte,PBL)为靶细胞,检测细胞膜上Fas的表达。人重组Fas配体(recombinanthumanFasligand,rhFasL)诱导细胞6～36h后用改良后的API等方法检测细胞凋亡及诱导凋亡过程中细胞周期蛋白的变化,探讨Fas介导的细胞凋亡与细胞周期的关系。结果显示:rhFasL诱导Molt-4、Jurkat细胞株和植物血凝素刺激进入细胞周期的PBL的凋亡具有细胞周期特异性并始动于G1期;而G0期PBL的细胞膜上虽然也有Fas的表达,但不能诱导细胞凋亡。研究还发现rhFasL诱导细胞凋亡时G1期的细胞周期蛋白D3明显升高,细胞周期蛋白E明显下降。以上结果表明rhFasL体外诱导的细胞凋亡发生在晚G1期,细胞凋亡的发生与细胞是否通过限制点进入细胞周期有关,细胞凋亡发生于晚G1期是G1期细胞周期蛋白E的下降和检测点的监督导致DNA受损的细胞不能通过G1/S交界的结果。     

The proteasome pathway destabilizes Yersinia outer protein E and represses its antihost cell activities

Pathogenic Yersinia spp. neutralize host defense mechanisms by engaging a type III protein secretion system that translocates several Yersinia outer proteins (Yops) into the host cell. Although the modulation of the cellular responses by individual Yops has been intensively studied, little is known about the fate of the translocated Yops inside the cell. In this study, we investigated involvement of the proteasome, the major nonlysosomal proteolytic system in eukaryotic cells, in Yop destabilization and repression. Our data show that inhibition of the proteasome in Yersinia enterocolitica-infected cells selectively stabilized the level of YopE, but not of YopH or YopP. In addition, YopE was found to be modified by ubiquitination. This suggests that the cytotoxin YopE is physiologically subjected to degradation via the ubiquitin-proteasome pathway inside the host cell. Importantly, the increased levels of YopE upon proteasome inhibition were associated with decreased activity of its cellular target Rac. Thus, the GTPase-down-regulating function of YopE is enhanced when the proteasome is inhibited. The stabilization of YopE by proteasome inhibitor treatment furthermore led to aggravation of the cytotoxic YopE effects on the actin cytoskeleton and on host cell morphology. Together, these data show that the host cell proteasome functions to destabilize and inactivate the Yersinia effector protein YopE. This implies the proteasome as integral part of the cellular host immune response against the immunomodulatory activities of a translocated bacterial virulence protein.     

The Yersinia enterocolitica type 3 secretion system (T3SS) as toolbox for studying the cell biological effects of bacterial Rho GTPase modulating T3SS effector proteins

The bacterial effector proteins IpgB(1) and IpgB(2) of Shigella and Map of Escherichia coli activate the Rho GTPases Rac1, RhoA and Cdc42, respectively, whereas YopE and YopT of Yersinia inhibit these Rho family GTPases. We established a Yersinia toolbox which allows to study the cellular effects of these effectors in different combinations in the context of Yersinia type 3 secretion system (Ysc)-T3SS-mediated injection into HeLa cells. For this purpose hybrid proteins were constructed by fusion of YopE with the effector protein of interest. As expected, injected hybrid proteins induced membrane ruffles and Yersinia uptake for IpgB(1) , stress fibres for IpgB(2) and microspikes for Map. By co-infection experiments we could demonstrate (i) IpgB(2) -mediated and ROCK-dependent inhibition of IpgB(1) -mediated Rac1 effects, (ii) YopT-mediated suppression of IpgB(1) -induced Yersinia invasion and (iii) failure of YopE-mediated suppression of IpgB(1) -induced Yersinia invasion, presumably due to preferential inhibition of RhoG by YopE GAP function. By infecting polarized MDCK cells we could demonstrate that Map or IpgB(1) but not IpgB(2) affects cell monolayer integrity. In summary, the Yersinia toolbox is suitable to study cellular effects of effector proteins of diverse bacterial species separately or in combination in the context of bacterial T3SS-mediated injection.     

Functional conservation of the secretion and translocation machinery for virulence proteins of yersiniae, salmonellae and shigellae.

Virulent bacteria of the genera Yersinia, Shigella and Salmonella secrete a number of virulence determinants, Yops, Ipas and Sips respectively, by a type III secretion pathway. The IpaB protein of Shigella flexneri was expressed in Yersinia pseudotuberculosis and found to be secreted under the same conditions required for Yop secretion. Likewise, YopE was secreted by the wild-type strain LT2 of Salmonella typhimurium, but YopE was not secreted by the isogenic invA mutant. Secretion of both IpaB and YopE required their respective chaperones, IpgC and YerA. In addition, yopE-containing S. typhimurium expressed a YopE-mediated cytotoxicity on cultured HeLa cells. YopE was detected in the cytosol of the infected HeLa cells and the amount of translocated YopE correlated with the degree of cytotoxicity. Both translocation and cytotoxicity were prevented by the addition of gentamicin. Treatment of HeLa cells with cytochalasin D prior to infection prevented internalization of bacteria, but translocation of YopE was still observed. These results favour the hypothesis that YopE is translocated through the plasma membrane by surface-located bacteria. We propose that virulent Salmonella and Shigella deliver virulence effector molecules into the target cell through the utilization of a functionally conserved secretion/translocation machinery similar to that shown for Yersinia.     

YopE of Yersinia, a GAP for Rho GTPases, selectively modulates Rac-dependent actin structures in endothelial cells

Yersinia spp. inject effector proteins ( Y ersinia o uter p roteins, Yop s ) into target cells via a type III secretion apparatus. The effector YopE was recently shown to possess GAP activity towards the Rho GTPases RhoA, Rac and CDC42 in vitro . To investigate the intracellular, ' in vivo ' targets of YopE we generated a Yersinia enterocolitica strain [WA(pYLCR+E)] that injects 'life-like' amounts of YopE as only effector. Primary human umbilical vein endothelial cells (HUVEC) were infected with WA(pYLCR+E) and were then stimulated with: (i) bradykinin to induce actin microspikes followed by ruffles as an assay for CDC42 activity followed by CDC42 stimulated Rac activity; (ii) sphingosine-1-phosphate to form ruffles by direct Rac activation; or (iii) thrombin to generate actin stress fibres through Rho activation. In WA(pYLCR+E)-infected HUVEC microspike formation stimulated with bradykinin remained intact but the subsequent development of ruffles was abolished. Furthermore, ruffle formation after stimulation with sphingosine-1-phosphate or thrombin induced production of stress fibres was unaltered in the infected cells. These data suggest that YopE is able to inhibit Rac- but not Rho- or CDC42-regulated actin structures and, more specifically, that YopE is capable of blocking CDC42Hs dependent Rac activation but not direct Rac activation in HUVEC. This provides evidence for a considerable specificity of YopE towards selective Rac-mediated signalling pathways in primary target cells of Yersinia .     

The cytotoxic protein YopE of Yersinia obstructs the primary host defence

It has previously been shown that the plasmid-encoded YopE protein of Yersinia pseudotuberculosis is a virulence determinant. In this study, HeLa cells, macrophages and mice were used as different model systems to determine the actual role of YopE in the virulence process. The YopE protein mediates a cytotoxic response on a confluent layer of HeLa cells. A prerequisite of this activity is that the pathogen binds to the cell surface. YopE also induces a cytotoxic response on mouse macrophages where it influences the ability of the pathogen to resist phagocytosis. Bacterial mutants defective in their ability to express YopE are avirulent after oral or intraperitoneal infection but virulent following intravenous injection. On the basis of these results, we propose a role for YopE in the virulence process of Yersinia.     

Intracellular targeting of exoenzyme S of Pseudomonas aeruginosa via type III-dependent translocation induces phagocytosis resistance, cytotoxicity and disruption of actin microfilaments

Exoenzyme S (ExoS) is an ADP-ribosyltransferase secreted by the opportunistic pathogen Pseudomonas aeruginosa . The amino-terminal half of ExoS exhibits homology to the YopE cytotoxin of pathogenic Yersinia . Recently, YopE was found to be translocated into the host cell by a bacteria–cell contact-dependent mechanism involving the ysc -encoded type III secretion system. By using an approach in which exoS was expressed in different strains of Yersinia , including secretion and translocation mutants, we could demonstrate that ExoS was secreted and translocated into HeLa cells by a similar mechanism to that described previously for YopE. Similarly to YopE, the presence of ExoS in the host cell elicited a cytotoxic response, correlating with disruption of the actin microfilament structure. A similar cytotoxic response was also induced by a mutated form of ExoS with a more than 2000-fold reduced ADP-ribosyltransferase activity. However, the enzymatically active ExoS elicited a more definite rounding up of the HeLa cells, which also correlated with decreased viability of the cells after prolonged infection compared with cells infected with strains expressing mutated ExoS or YopE. This suggests that ExoS can act through two different mechanisms on the host cell. The expression of ExoS by Yersinia also mediated an anti-phagocytic effect on macrophages. In addition, we present evidence that extracellularly located P. aeruginosa is able to target ExoS into eukaryotic cells. Taken together, our data suggest that P. aeruginosa , by analogy with Yersinia , targets virulence proteins into the eukaryotic cytosol via a type III secretion-dependent mechanism as part of an anti-phagocytic strategy.     

Intracellular membrane localization of pseudomonas ExoS and Yersinia YopE in mammalian cells

ExoS (453 amino acids) is a bi-functional type-III cytotoxin of Pseudomonas aeruginosa. Residues 96-233 comprise the Rho GTPase-activating protein (Rho GAP) domain, while residues 234-453 comprise the 14-3-3-dependent ADP-ribosyltransferase domain. Residues 51-72 represent a membrane localization domain (MLD), which targets ExoS to perinuclear vesicles within mammalian cells. YopE (219 amino acids) is a type-III cytotoxin of Yersinia that is also a Rho GAP. Residues 96-219 comprise the YopE Rho GAP domain. While the Rho GAP domains of ExoS and YopE share structural homology, unlike ExoS, the intracellular localization of YopE within mammalian cells has not been resolved and is the subject of this investigation. Deletion mapping showed that the N terminus of YopE was required for intracellular membrane localization of YopE in CHO cells. A fusion protein containing the N-terminal 84 amino acids of YopE localized to a punctate-perinuclear region in mammalian cells and co-localized with a fusion protein containing the MLD of ExoS. Residues 54-75 of YopE (termed YopE-MLD) were necessary and sufficient for intracellular localization in mammalian cells. The YopE-MLD localized ExoS to intracellular membranes and targeted ExoS to ADP-ribosylate small molecular weight membrane proteins as observed for native type-III delivered ExoS. These data indicate that the YopE MLD functionally complements the ExoS MLD for intracellular targeting in mammalian cells.     

Crystal structure of the Yersinia pestis GTPase activator YopE

Yersinia pestis, the causative agent of bubonic plague, evades the immune response of the infected organism by using a type III (contact-dependent) secretion system to deliver effector proteins into the cytosol of mammalian cells, where they interfere with signaling pathways that regulate inflammation and cytoskeleton dynamics. The cytotoxic effector YopE functions as a potent GTPase-activating protein (GAP) for Rho family GTP-binding proteins, including RhoA, Rac1, and Cdc42. Down-regulation of these molecular switches results in the loss of cell motility and inhibition of phagocytosis, enabling Y. pestis to thrive on the surface of macrophages. We have determined the crystal structure of the GAP domain of YopE (YopE(GAP); residues 90-219) at 2.2-A resolution. Apart from the fact that it is composed almost entirely of alpha-helices, YopE(GAP) shows no obvious structural similarity with eukaryotic RhoGAP domains. Moreover, unlike the catalytically equivalent arginine fingers of the eukaryotic GAPs, which are invariably contained within flexible loops, the critical arginine in YopE(GAP) (Arg144) is part of an alpha-helix. The structure of YopE(GAP) is strikingly similar to the GAP domains from Pseudomonas aeruginosa (ExoS(GAP)) and Salmonella enterica (SptP(GAP)), despite the fact that the three amino acid sequences are not highly conserved. A comparison of the YopE(GAP) structure with those of the Rac1-ExoS(GAP) and Rac1-SptP complexes indicates that few, if any, significant conformational changes occur in YopE(GAP) when it interacts with its G protein targets. The structure of YopE(GAP) may provide an avenue for the development of novel therapeutic agents to combat plague.     

The RhoGAP activity of the Yersinia pseudotuberculosis cytotoxin YopE is required for antiphagocytic function and virulence

A variety of pathogenic bacteria use type III secretion pathways to translocate virulence proteins into host eukaryotic cells. YopE is an important virulence factor that is translocated into mammalian cells via a plasmid-encoded type III system in Yersinia spp. YopE action in mammalian cells promotes the disruption of actin filaments, cell rounding and blockage of phagocytosis. It was reported recently that two proteins with sequence similarity to YopE, SptP of Salmonella typhimurium and ExoS of Pseudomonas aeruginosa, function as GTPase-activating proteins (GAPs) for Rho GTPases. YopE contains an 'arginine finger' motif that is present in SptP, ExoS and other Rho GAPs and is essential for catalysis by this class of proteins. We show here that a GST-YopE fusion protein stimulated in vitro GTP hydrolysis by the Rho family members Cdc42, RhoA and Rac1, but not by Ras. Conversion of the essential arginine in the arginine finger motif to alanine (R144A) eliminated the in vitro GAP activity of GST-YopE. Infection assays carried out with a Yersinia pseudotuberculosis strain producing YopER144A demonstrated that GAP function was essential for the disruption of actin filaments, cell rounding and inhibition of phagocytosis by YopE in HeLa cells. Furthermore, the GAP function of YopE was important for Y. pseudotuberculosis pathogenesis in a mouse infection assay. Transfection of HeLa cells with a vector that produces a constitutively active form of RhoA (RhoA-V14) prevented the disruption of actin filaments and cell rounding by YopE. Production of an activated form of Rac1 (Rac1-V12), but not RhoA-V14, in HeLa cells interfered with YopE antiphagocytic activity. These results demonstrate that YopE functions as a RhoGAP to downregulate multiple Rho GTPases, leading to the disruption of actin filaments and inhibition of bacterial uptake into host cells.     

Delineation and mutational analysis of the Yersinia pseudotuberculosis YopE domains which mediate translocation across bacterial and eukaryotic cellular membranes.

Pathogenic yersiniae deliver a number of different effector molecules, which are referred to as Yops, into the cytosol of eukaryotic cells via a type III secretion system. To identify the regions of YopE from Yersinia pseudotuberculosis that are necessary for its translocation across the bacterial and eukaryotic cellular membranes, we constructed a series of hybrid genes which consisted of various amounts of yopE fused to the adenylate cyclase-encoding domain of the cyclolysin gene (cyaA) of Bordetella pertussis. By assaying intact cells for adenylate cyclase activity, we show that a YopE-Cya protein containing just the 11 amino-terminal residues of YopE is efficiently exported to the exterior surface of the bacterial cell. Single amino acid replacements of the first seven YopE residues significantly decreased the amount of reporter protein detected on the cell surface, suggesting that the extreme amino-terminal region of YopE is recognized by the secretion machinery. As has recently been shown for the Y. enterocolitica YopE protein (M.-P. Sory, A. Boland, I. Lambermont, and G. R. Cornelis, Proc. Natl. Acad. Sci. USA 92:11998-12002, 1995), we found that export to the cell surface was not sufficient for YopE-Cya proteins to be delivered into the eukaryotic cytoplasm. For traversing the HeLa cell membrane, at least 49 yopE-encoded residues were required. Replacement of leucine 43 of YopE with glycine severely affected the delivery of the reporter protein into HeLa cells. Surprisingly, export from the bacterial cell was also not sufficient for YopE-Cya proteins to be released from the bacterial cell surface into the culture supernatant. At least 75 residues of YopE were required to detect activity of the corresponding reporter protein in the culture supernatant, suggesting that a release domain exists in this region of YopE. We also show that the chaperone-like protein YerA required at least 75 YopE residues to form a stable complex in vitro with YopE-Cya proteins and, furthermore, that YerA is not required to target YopE-Cya proteins to the secretion complex. Taken together, our results suggest that traversing the bacterial and eukaryotic membranes occurs by separate processes that recognize distinct domains of YopE and that these processes are not dependent on YerA activity.